Gas purifying apparatus



Det 31, 1945 A H. T. HoLzwARTH 2,413,324

GAS PURIFYING APPARATUS Filed June 8, 1940 3 Sheets-Sheet 1 2 ff'z.

4 L l la' a; 2 zfl INVENTOR. 7`. HOLZ WA/P 7`H A TTORNE YJ Dec. 3l, 1946. H. T. HoLzwARTH GAS PURIFYING APPARATUS Filed June 8, 1940 3 sheets-sheet ,2A

I w" Y INVENTOR. l'/.4 7'. HOLZWAR TH ATTORNEYJ` Dec. 3l, 1946.

CENTR/PETAL CCELE//V 0F GAS H. T. HOLZWARTH GAS PURIFYING APPARATUS Filed June 8, 1940 Ill 2"? 3 Sheets-Sheet 5 l l am n lao ha I l dan MM INVENTOR. liv?? HOLZWA? TH A'I'TORNEYJ` Patented ec. 3l., 1946 GAS PURIFYING APPARATUS Hans Theodor Holzwarth,

signor to Holzwarth Gas cisco, Calif., a corporati Woodmere, N. Y., as-

Turbine Co., San Franon of Delaware Application June 8, 1940, Serial No. 339,449 In Germany June 9, 1939 2 Claims.

The present invention relates to the purification of gases by the removal of oil, water droplets, dust and other particles suspended therein.

It is the general object of the invention to provide a gas purifying device Which is simple and compact in construction, highly efcient in operation, and inexpensive to manufacture, and also one which utilizes the available space with practically no waste, and possesses an extremely low resistance.

The apparatus of the present invention is of the type in which the particles preferably to be removed (in the case of dust particles, after a previous injection of atomized liquid, such as Water, for Weighting the particles) are subjected to the action of centrifugal force to cause them to be flung to the outer periphery of their path of travel, the particles being collected in suitable discharge openings arranged along such outer periphery.

The present invention is an improvement over the construction shown in the copending application of Hans Holzwarth, Serial No. 181,562, filed December 24, 1937, which issued as Patent No. 2,271,642 on February 3, 1942. As in the apparatus of such prior application, the separation of suspendedparticles is effected in the device of the present invention by causing the gas to flow along one or more channels of curvilinear form within which it is accelerated, the particles being thus hurled by centrifugal force to the outer periphery of their path, where they are collected and removed from the gas streams. However, whereas in the prior apparatus the pitch of the coiled channels, or the inclination of the channel side walls with respect to the axis about Which the channels are coiled, remains constant, in the apparatus of the present invention the channels are coiled in such manner that their pitch, or the Wall inclination, changes more or less constantly. Thus the pitch of the median lines of the channel or channels gradually decreases to an intermediate point and then graduallyincreases to or toward the discharge ends of the channels; while the inclination of the side walls with respect to the central longitudinal axis, on the other hand, increases to such intermediate point and then decreases. By the provision of a varying pitch, the curvilinear channels are each provided with an inlet section of gradually decreasing cross-section which terminates in a region of minimum cross-section, from` which the outlet or diiuser section gradually increases in cross-section to the discharge end of the apparatus. These channels may be termediate portion of minimum cross-sectional,

area, all being comprised within the curvilinear or coiled channel.

Previous attemptslto obtain a high degree of acceleration of the gases within a curvilinear channel by the provision of a region of reducedV cross-Section have been carried out by milling the channels along the periphery of a thick walled cylinder, the height of the side walls of the channels remaining constant, as disclosed, for example, in the above mentioned application. This resulted in relatively thick walls, which both increased the Weight of the apparatus and reduced the effective peripheral ilow area. Also, the cost of constructing such an apparatus by machining or even by casting supplemented by machining was quite high. Another method of creating the region of reduced cross-section was to coil the channels about a conical core member, the height of the side walls ofV the channels thus decreasing While the distance between the walls remained constant. This type of apparatus was likewise difficult and expensive to manufacture.

In accordance with the present invention, sheet metal strips of identical form and of uniform height are employed for dening the channels, the strips being welded, soldered or secured in any other suitable manner to a core member which is preferably of cylindrical form, the strips, which form the side walls of the channels, being secured in such manner to the core member that the angle which they make with the central longitudinal axis of such member gradually increases to the region at which it is desired that the cross-section of the channels shall be at a minimum, and then increases to, or approximately to, the discharge end of the device. This change in the inclination of the walls by itself produces the regions of minimum cross-section in the coiled channels which are necessary forv eiecting increase in the velocity of the gases.

By such arrangement, a highly eicient Venturi.

effect, is produced, while at the same time, practicallyY the whole annular space between the core member and its external housing is available for the flow of gases, the thin 'side walls occupying very little space. y

My apparatus may thus be regarded as consisting essentially of one or more thin-walled Venturi-like tubes coiled with rst a decreasing and then an increasing pitch, the region of minhigh degree of acceleration of the gas, a's will,

be explained more in detail hereinbelow.

A satisfactory form of the invention is shown by way of illustration on the accompanying drawings, wherein Fig. 1 shows a vertical section through` an apparatus constructed in accordance with the in-l Venton, the section being taken along the'line I-I of Fig. 2;

Fig. 2 is an end View of the spider frame uponv which the core member is seated;

Fig. 3 represents the development ofy the Isurface, of the core member andA shows the change in'the inclination of the sheet metal side walls ofthey channels or, what is the same thing, the change in the pitch of the coiled channelsand the resulting changes in cross-section of. the channels; and

Fig.; 4 illustrates graphicallyv the changes in the,I angle of inclination of the channel side walls (projected against the longitudinal axis vof the core member) along the length of the core body, measured in the direction of the longitudinal axis;"a nd'shows also the centripetal accelerations occurring in thecoiled`channels in dependence upon the ,changes lin suchv angle.

` Asv shown in Fig. 1,' my improvedgas purifying apparatus comprises an outer. housing I provided with discharge openings 2'., 2 for the particles being separated, as will be explained hereinbelow,'theparticles collecting-in the annular chambers A rand lflowing off-throughfthe discharge conduit'sS. The housing I is connected at one end to. .a 'tubular member 5A througli'which theI gasesV topez treated are fed thereto. Where the gases are to be freed. from dust particles, the latter may be weighted with water droplets in any suitable manner;Y thus Ythe tube -5 may contain or be shaped inthe form of agas expansion nozzle and be providedl with injection nozzles for the wash liquid, as` disclosed in the aboveementioned patent; At its other endthe housing is connected to atubular section 6, which leads oif the purified gas. The apparatus shownin Fig, 1 is designed to be supported with its axis horizontal, the discharge openings 2 being at thelower crown line. The openings 2f and 2 and the discharge conduits 3 can,` however, be modified in an cbviousvmannerfto enable the device to be used in the` upright position.

lnlthehousing I, there is located a core member 1 of smaller external'diameter than the internal diameter of the housing, so as to provide an -annular space I therebetween. The core member is supported against the now pressure of y the gases entering atl 5by an annular spider frame t provided-with spaced ribs 3 forming a seat for the conical end l" of thecore member.V t The.

ribs 8,( are widely yspaced asshown in Fig. 2, so thatno resistance isoffered to the flow ofthe gases passing thrcughthe housing I. A conical section 'I at the inlet end of thecoremember aids in distributing the gases to the annular space Iffa'V dalso effects gradual increase in the'velocity ofgthe'gases as they approach such annular space The present invention is concerned with the manner in which the annular space I' is divided into a number of channels within which the velocity of the gas streams is increased and likewise the centrifugal forces acting upon the particles to be removed. Increase in the velocity of the gases requires that the cross-section of the channels be reduced, preferably intermediate their ends. According to the present invention,

the core member 'I is provided with a plurality of sheet metal strips 9 which are united therewith by soldering, welding, or in any other suitable manner, so that separate channels IIJ are formed. The height ot the metal strips is such that a substantially gas-proof contact with the inner surface of thehousing I is established, the housingforming the outer wall of all of the channels. These sheet meta-l strips constitute the channel side walls and are identical in construction. Whereas, heretofore, the channels, i. e. the median lines of the channels, were given a uniform pitch, in accordance with the present invention, the sheet metal walls 9 are so mounted upon the member IQ that their inclination with respect to the longitudinal axis II-II of the member I0 varies along the length of such member, As can be seen from Figs. l and 3, this inclination, which is indicated by. way of example by the angle a in Fig. l between the sheet metal strip 9 and the longitudinal axis II-II, increases continuously from the inlet end portion I0', the depth ofthe channel, indicated at.I2, and measured in the radial direction with respect to the said axis, remaining unchanged. The increase in the mentioned angle continues to the region of narrowest channel cross-section, indicated approximately at IG." and from such point, the inclination gradually decreases to the discharge end portions I3 of the channels. The pitch of the several channels (6 channels are present in the construction illustrated) thus decreases to the region of minimum cross-section and then again increases tothe discharge end.

The curve representing the angle a in Fig. 4, wherein the abscissaev represent distances along thelongitudinalaxis of the apparatus measured from the inlet end, showsY clearly that by reason of the sharp initial curvature of the sheet metal strips 9, such angle increases very rapidly to a value ofabout 45 and thereafter more gradually to about In thediffusor section of the channels, it decreases very rapidly.

It will be noted that the angularity of the median lines of the channels with respect to the longitudinal axis continues to increase beyond the inlet portion Hl', and in fact up to a region approximately midway between the ends of the channels, there preferably being discharge openings both in advance ofand beyond the region of minimum channel cross section, as will be explainedbelow in connection with Fig. 4. It will also be observed that my improved apparatus can be made of such small axial length that the angularV dimension of each complete channel is approximately only about 360, that is, only about one completeturn. From this fact, the extraordinary compactness of the illustrated structure will be more readily realized,

The variation in-the pitch of the walls 9- not only.. bringsabout automatically `the necessary reductionin the crossfsection of the channels and a corresponding increase in the velocity of the gases 'and in the centrifugal forces actingon the particles to be removed, but produces a still further. result which practically doubles the efflciency of the apparatus as compared with known devices. An idea of the surprising results attainable with the apparatus of the present invention will be gained from the fact that it is possible tc'secure in such apparatus without difficulty centripetal accelerations of the order of about 3000 times the acceleration of gravity.

.This additional result is due to the reduction in the effective radius of curvature which results from the decrease in the pitch of the channels. As is known, the centripetal acceleration to which a particle of matter is subjected is proportional on the one hand to the square of its velocity, while on the other hand it stands in inverse relationship to the radius of curvature of the path which it describes at the moment under consideration. It would therefore appear to be obvious, in Vview of the preponderatinginiiuence of the velocity, to raise the velocity to the greatest possible degree. It must, however, not be overlooked that velocity and pressure stand in a iixed mutual relationship, and that the gas velocity corresponds to a deiinite pressure drop which must be available. In addition, the gas velocity cannot be increased at will because of the resulting losses. It has been possible to reduce the losses by reconverting the produced velocity again into pressure, after completion of the separation, in the diffusor section of the channel, which is constructed in the form of a Venturi nozzle. However, the conversion of the pressure energy into flow energy and the repeated conversion of the iiow energy into pressure energy is associated with unavoidable losses, to which must still be added the quite considerable friction, elbow and whirling losses which inevitably attend the flow of gases at high velocity. There thus results in a given condition of the gas to be purified, according to pressure and flow weight, an upper limit for the greatest velocity to be realized in the separation of the particles, and for the distance over which it may come into use, and whose further increase would only lead to a reduction in the economy of the process. The flow cross-sections to be made available are fixed by this limiting velocity for a given gas volume to be purified per unit of time. A

The centripetal acceleration depends, as already mentioned, not only upon the velocity, but also upon the radius of curvature of the path of the particles to be separated; in other words, upon the radius of curvature of the median line of the coiled channel. The smaller this radius of curvature is, the greater will be the centripetal acceleration. As, however, the iiow cross-sections for a given gas volume and pressure are fixed, the reduction of the radius of the core cannot be carried to any desired extent, since such reduction must be compensated by a corresponding increase in the radial depth of the channels to maintain the required flow area, and the radial depth cannot be increased at will for the reasons given below. This circumstance works out all the more disadvantageously since the radius that enters into the computation of the acceleration is not directly the radius of the core (or more exactly, the radius of the imaginary cylindrical surface on which the median lines of the channels lie, which radius is larger than that of the outer surface of the core), but rather the radius of curvature of the coiled channels, which latter radius is always larger than the radius even of the median lines, for the reason that the channels are arranged in helical fashion. The effective radius of curvature of the coiled channels corresponds not to the radius or to the radii of the surface of the body of revolution upon which the median lines Vof the coiled channels lie, but tothe quotient o1 this radius and the'square of the sine of that angle which the coiled channels make with the longitudinal axis of such surface of the body of revolution at any point. IfV this angle i590, then the channels run in a plane perpendicular to the longitudinal axis under consideration, and the effective radius of curvature of the channels assumes the most favorable minimum value equal'to the radius of curvature of the imaginary cylinder above referred to, but at the same time the cross-section of the channels will become equal to zero, so that the realization of the theoretically smallest radius of curvature would, for this reason, be excluded from practical consideration. The smaller, on the other hand, the angle becomes, the greater do the channelV cross-sections become the greater also their radius of curvature. Since a definite channel cross-section must be realized for the reasons already mentioned, there thus results also a practically attainable maximum value for the angle, and thus a practically attainable minimum effective radius of curvature of the channels, which minimum radius is considerably larger than the radius of the core member,

This mutual relationship between the channel cross-section and effective radius of curvature could be avoided by increasing the depth of the channels measured along ythe perpendicular to the longitudinal axis of the core or surface about which the channels are coiled, i. e. in the radial direction.

But eventhis possibility is limited, being subject to the mutual relationship between the iiow velocity of the gases on vthe one hand and the viscosity of the gases and the centrifugal forces on the other. For, corresponding to the velocity of the gases, there is available to those particles, which by reason of their position in the region of the core 7, must traverse the whole radial channel depth before they can reach the outlets 2', 2" arranged at the outer channel periphery, only a quite definite, extremely small time interval for such purpose. to be separated, the more important a role does the viscosity of the gas play, and this must be overcome by the particles under the influence of the centrifugal forces exerted thereon to enable them to traverse the indicated path. Upon the basis of exact calculations, confirmed by experiment, a surprisingly large reduction of the advancing velocity of the particles was found to accompany a reduction in the size of the particles. If, therefore, the radial depth of the coiledv channel is too great, then a considerable portion of the particles simply has no longer sufficient.

time during the strongly accelerated flow through the coiled channel to traverse the radial channel depth within the time interval determined by the flow Velocity and the length of the channel, and reach the discharge openings 2', 2". If, therefore, the eciency of separation or purification is to be be maintained, a limited radial depth of the coiled channels must not be exceeded. This maximum depth can be determined either by simple experiment or by calculation,

The construction described above embodies my discovery that a mutual relationship exists between the friction, elbow and whirling losses on the one hand and the possibility on the other hand of suitably dimensioning the distance upon which the particles to be separated are subjected 'Ihe smaller the particles to a. particularly high centrifugal action. The dimension` is suitable when it makes possible that a particle lying evenin the neighborhood of the core, iinds enough time ata given velocity and viscosity of. the gases on the one hand and with a given channel dimensioning on the other to reach the discharge opening under the iniiuence of this greatest centripetal acceleration. For only in this way can the indicated losses be reduced to a value which does not prejudice the economy of. the, gas purification. If the place of greatest centripetal acceleration, which is attainable only by `suitable dimensioning of the effective radius of curvature and with it the inclination o'f the channels tothe longitudinal axis of the core, as well as ofthe flow velocity of the gases, were embodied in a larger channel length, as would occur, for example, inthe case of coiled channel constructions of uniform but small pitch, then the elbow losses andl likewise the whirling and friction losses would multiply in correspondence with the long distance over which the high flow velocity and the small radius of curvature are applied, without gaining anything in this way. According to the principles of the present invention, the distance over which the particles to be separated are subjected to a particularly high centrifugal force, i. e. the stretch over which the radius of curvature is small, is made no greater than is necessary to enable the particles, even when located at the inner periphery of the channels, thatis, in the neighborhood of the core, and with a not too largeA radial channel depth and with a given viscosity Vand flow velocity of the gas particles, to be driven with certainty through the gas to the outer periphery of the coiled channel Vandv be flung into the collecting openings for the particles.

TheA reduction in the pitch of the channels, with the accompanying decrease in the radius of curvature to a value more nearly equal to the radius of the core member 1, thus causes sufficient increase of the acceleration of the gases to insure that practically all particles will reach the outer periphery ofthe channels; and since the region of minimum pitch is of only small extent, it does not cause any material losses.

As shown in Fig, 1, the radial depth of the several channels is made smallenough to enable particles at the inner radius of the channels to reach the limit of the outer radius, and hence the discharge openings 2, 2 by making the diameter of the core i relatively large with respect to the inner diameter ofthe housing I. Thus the core diameter may be made considerably more than half the inner diameter of the housing. In the preferred construction shown in Fig. 1, the annular space l2 is relatively narrow in comparison with the yinner radius of the housing. Thereby higher gas velocities are created within the channels it; while at the same time the reduction in pitch within only about one turn of the channels (i. e. within an angular distance effective of about 360) is sufcient to create `the necessary centrifugal forces to cause the particles to reach the discharge openings within the limited time allowed for their removal. This accounts for the fact that the apparatus of the invention is able to provide as eiicient a purification of gases as, if not a higher degree of purication than, known separators employing Archimedean screws having many turns of-uniorm pitch.

If the reduction in` cross-section in the initial or-inlet portionof the channels, produced by the increase -in the inclination of the channely walls,

corresponds lto the. cross-,section reduction in a tubular 'nozzle :(of circular crossfsection) with a conical .angle Vof about 9 to the axis, and correspends in the intermediate portion up to the narrowest cross-section to a. tubular nozzle with aconical angle of about 1, while the cross-sectional increase in the diffusor section of the channel .corresponds .to the cross-sectional increase of a tubular nozzle with approximately a 3 conical angle, there .will be obtained,.as.experiments have shown, a particularly favorable relationship,

The. curve b in Fig, 4 wherein 'the ordinates represent centripetal gas acceleration, illustrates the..extraordinarily high accelerations which can besecured by the narrowing of the channels with simultaneous decrease in the eiective radius of curvature. As shown by the graph, an acceleration ofl about three thousand times the acceleration, of gravity can be obtained. In contrast to devices with uniform inclination, that is, with constant rangle a, and as shown by the graph, not only can the initial angle for the coiled channels be made smaller, but there occurs additionally, up to the narrowest cross-section, a further increase-of the angle of inclination up to the abovementioned angle of 65. Since the sine of the angle increases correspondingly, the quotient of the` core radius and the square of the sine (representing the effective radius of curvature) decreases, whereby an increase of the centripetal vaccelerations to about double results. In addition, the manufacture of this type of device is simplified and made cheaper as against the prior constructions; moreover they occupy less space than the latter and have a smaller Weight.

In Fig. 4, there is indicated at Which points the discharge openings 2', 2" are arranged. Three of theopenings 2', 2" are arranged in advance of the narrowest cross-section I0", while two channels suffice, after the point of greatest centripetal acceleration, to aiord the last particles opportunity for separation.

It will be understood that suitable sealing devices will be associated with the discharge outlets 2l and 2" to insure against the escape of the gases, a liquid trap, for example, in the form of a siphon, being highly satisfactory. This type of sealing is disclosed in the above mentioned application, and as it forms no part of the present invention, has not been illustrated in the drawings.

It will 'be noted that the discharge openings 2', @2" are in the form of more or less annular slits which lie in planes which are approximately normal vto the longitudinal axis of the apparatus. Each of the slits in the embodiment shown in Fig. 1 intersects a plurality of channels l0, IU. The discharge conduits 3 leading from the discharge Aopenings or slits, as will be clear from Fig. .1, are separate from each other, i. e. are not in communication, externally of the channels l0, l0" and the housing l, so that different pressures may prevail in these conduits. It will thus be obvious that the discharge openings and discharge conduits do not connect portions of the ohannels'which are of differentpressures, so that the proper pressure variations along` the length of theapparatus are maintained.

If desired, the discharge ends of the channel walls 9 may be so constructed and mounted on the corezas tolie at a slight angle to the longitudinal axis of the core so as to give a slight twist tothe streams of gasesdischarging from the channels.

fris-already indicated, the above described apparatus is suitable for the separation both of liquid droplets, as Well as of solid particles; and in the case of the latter, and particularly where they are of very small size, it is preferable to inject an atomized wash liquid into the stream of gases in advance of the separator mechanism in order to weight the particles. While the separator has been shown as comprising a plurality of channels, it will be obvious that for smaller capacities, fewer channels and even a single channel, constructed in the manner above described, can be employed.

Variations from the speciiic details hereinabove described by way of illustration may be resorted to Within the scope of the appended claims Without departing from the principles or spirit of the invention as defined in the subjoined claims.

I claim:

l. Apparatus for the purification of gases by removal of liquid or solid particles suspended therein, comprising an approximately helical channel through which the gases to be puried travel, the inclination of the side walls of the channel with respect to the longitudinal axis about which the channel is curved being of varying degree, and increasing from the inlet end of the channel to an intermediate section of the channel where a region of narrowcst channel cross-section is provided, the inclination of the Walls then decreasing from such narrowest crosssection toward the discharge end of the channel, and discharge openings in the outer periphery of the channel into which the suspended particles are iiung by centrifugal force, the discharge openings comprising a series of axially spaced annular slits in the outer Wall of the channels,

2. Apparatus for the purification of gases by removal of liquid or solid particles suspended therein through the action of centrifugal force, comprising an outer housing adapted to be connected to a gas conduit, a plurality of strips heli cally disposed Within said housing to form Venturi-like channels coiled in approximately helical fashion, the median line of each of the channels making increasing and then decreasing angles with the longitudinal axis of the housing from the inlet toward the discharge end of the latter, and discharge openings for the suspended matter located in the outer Walls of the respective channels, the discharge openings comprising annular slits in the outer wall of the channels, said slits lying in planes substantially normal to the'longitudinal axis and each slit intersecting a plurality of channels.

HANS THEODOR HOLZWARTH. 

